The projects proposed are designed to study the structure and immunoregulatory role of the gene products in the I region of the mose H-2 complex. Our first specific aim is to complete the genomic cloning of the I region. The focus will be to clone the genomic DNA between H-2K and I-A Beta using cosmid libraries and the technique of chromosome walking. These clones will be examined for the presence of genes which have been genetically mapped to Ia but for which no protein product has been isolated. The completion of the cloning of the I region will provide answers as to the number of genes encoded in this region and possibly their function. The second specific aim will be to determine the nature of the specific interaction between Ia and the T cell. Since helper T cells only recognize antigen in the context of the appropriate Ia antigen, Ia plays a crucial role in this cell-cell interaction. By combining recently developed transfection procedures with in vitro mutagenesis techniques, we will alter the gene products for I-A and I-E before introducing them into antigen presenting cells and then measure their ability to functionally interact with T cells. The third specific aim is to determine if I-A or I-E expressed on B cells is capable of delivering a signal to the B cell which may in part be responsible for its activation. To successfully answer this question, we will express altered Ia antigens in small resting B cells and determine if the B cells can still be activated in the presence of antigen and T helper cells. The delivery system we propose to use for the expression in B cells is vaccinia virus.